Constant speed motor regulating lamp dimming circuit



June 30, 1970 E, BABCOCK 3,518,486

CONSTANT SPEED MOTOR REGULATING LAMP DIMMING CIRCUIT Filed Nov. 20, 196'? Patented June 30, 1970 United States Patent Ofice 3,518,486 CONSTANT SPEED MOTOR REGULATING LAMP DIMMING CIRCUIT Robert E. Babcock, Hendersonville, N.C., assignor to General Electric Company, a corporation of New York Filed Nov. 20, 1967, Ser. No. 684,314 Int. Cl. Gf 1/00; H05b 37/02 U.S. Cl. 315-194 Claims ABSTRACT OF THE DISCLOSURE It is an object of the invention to provide an improved dimming system for gaseous discharge lamps.

It is another object of the invention to provide a controlled lamp dimming system of the above type which avoids extinguishing of the lamp during the dimming operation.

It is a particular object of the invention to provide a dimming system of the above type which is applicable to phase control lamp operating circuits, especially those incorporating controlled semiconductor switching means.

It is still another object of the invention to provide a dimming system of the above type utilizing a constant speed motor operating a potentiometer.

Other objects and advantages will become apparent from the following description and the appended claims.

With the above objects in view, the present invention in a preferred embodiment relates to a lamp control circuit comprising, in combination, an alternating current source, gaseous discharge lamp means energized by the alternating current source, phase controlled switching means connected between the alternating current source and the gaseous discharge lamp means for controlling the energy supplied to the lamp means, actuating means connected to the alternating current source and the switching means for controlling the operation of the latter means, and controlled dimming means connected to the actuating means for varying the energy supplied to the lamp means for selectively dimming and brightening the latter without extinguishing the same.

In a particular embodiment, the controlled dimming means comprises potentiometer means and a reversible constant speed motor for adjusting the potentiometer means at a predetermined rate.

The invention will be better understood from the following description taken in conjunction with the accompanying drawing, in which:

The single figure is a circuit diagram of a preferred embodiment of a lamp control circuit with a dimming circuit therefor constructed and arranged in accordance with the invention.

Referring now to the drawing, there is shown a phasecontrolled switching circuit for controlling the current and voltage applied to a lamp load 1, which in a typical case to which the invention is applicable is a sodium vapor gaseous discharge lamp, the lamp being connected to terminals 2 of a source of alternating current, e.g., 120 or 240 volts, by conductors 3 and 4. Arranged in series with lamp 1 is a triac 5, which may be described as an alternating current semiconductor controlled switch having a single control electrode 5a which, when gated, causes the switch to conduct current in the direction as indicated by the forward bias condition of the semiconductor. A triac may also be described as a bidirectional triode for gate control of alternating current power.

The signal generating or actuating circuit comprises series-connected resistance 10 and charging capacitor 11 corrpected across terminals 2, thereby synchronizing the signal generating function with the source voltage.

The particular phase-controlled switching means and the signal generating or actuating circuit shown in the drawing is disclosed and claimed in co-pending applicatiori Ser. No. 646,871, filed June 19, 1967, in the name of "R. E. Babcock, and assigned to the same assignee as the present invention. The disclosure thereof is accordingly incorporated by reference herein.

As disclosed in the co-pending application, the actuating circuit further comprises a solid state symmetrical (i.e:,, bi-laterally conducting) voltage sensitive switch 7 which in the embodiment shown is connected at one side to control electrode 5a and at the other side to the junction of charging capacitor 11 and resistor 10. Switch 7 may also be described as a diac trigger, and more specifically as a diffused silicon bi-directional trigger diode. This deigice becomes conductive only upon application of a predetermined voltage thereon and is roughly equivalent to a neon glow lamp, but differs therefrom in beinga solid state device and, further, breaks down and operates at .lower voltages than the neon glow lamp. As shown, diac 7 is effectively connected in series discharge relation with capacitor 11 and control electrode 5a and serves therewith to provide a discharge loop when the voltage on: capacitor 11 reaches the breakdown level of diac 7. Thus, when a control signal is applied to electrode 5a by the: actuating circuit on each half cycle, triac 5 is gated through its control electrode 5a so as to conduct in opposite'directions on alternate half cycles. The control of the. delay or advance in the time of the alternating current input cycle at which the control signal impulse is applied to render the triac conductive, thereby dictating the.v load power level, is known as phase controlling. Phase control actuating means of similar function are disclosed in U.S. Pats. 3,249,807 and 3,344,310, both in the name of J. A. Nuckolls and assigned to the same assignee as the present invention.

In the illustrated embodiment, the switch actuating c'ircuit also comprises resistance 17 connected between the load side of triac 5 and the junction of capacitor 11 and resistance 10. Typically, resistance 17 is lower in value than that of resistance 10. In this arrangement, resistance 17 serves both as a component of the actuating circuit which includes capacitor 11 and resistance 10, and as a feedback component for stabilizing the load current. The control circuit further comprises a step-up transformer 6 connected in series between triac 5 and lamp 1, and serving as a combined lamp ballast and high voltage transformer. Connected across lamp 1 is charging capacitor 20 which is connected at one terminal to the transformer tap and at its other terminal to line conductor 4 by a resistance 21 and inductor 23. Capacitor 20 thus provides a charge path for drawing energizing current to the primary of transformer 6 when triac 5 is fired.

In the above described circuit arrangement, the trigger pulse timing and generating circuit comprises capacitor 11 in series with an effective resistance consisting of resistance 17 and resistance 10. This effective resistance operates by resistance 17 being placed in parallel with resistance 10 prior to firing of triac switch 5 and in parallel with the capacitor 11 branch for the remainder of the current conducting half cycle. This effective charging resistance and switching arrangement provides for rapid charging of capacitor 11 to enable triac switch 5 to be potentially fired early during the half cycle. However, after triac firing, this arrangement provides a shunting path for capacitor 11, thereby limiting the follow-through 60 cycle current that flows through diac 7.

On any given half cycle in the operation of the described circuit, capacitor 11 charges through resistance and resistance 17 in parallel to a voltage which reaches the breakdown potential (typically 32 volts) of diac 7, which then becomes conductive. Capacitor 11 then'discharges through diac 7 and a signal pulse is applied to control electrode 5a. When triac switch 5 becomes conductive, the operation of the discharge loop comprising triac switch 5, capacitor 20 and the primary of transformer 6 produces high frequency pulses having a voltage which is approximately that of the instantaneous line voltage, the pulses being placed on transformer 6 which then steps up the voltage to a high level, e.g., about 3.5 kilovolts, for starting lamp 1. Once lamp 1 has ignited, the high voltage generating circuit becomes partially deenergized by action of the lamp load impedance becoming low enough to load or dampen the above described high voltage switching mechanism.

The circuit also includes a device for compensating for input voltage variations which comprises photo-conductor 41, such as a cadmium sulfide photocell, connected across capacitor 11, and a small incandescent lamp 42 with series resistances 43 and 44 connected across supply lines 3 and 4, incandescent lamp 42 being arranged so that its light is incident on photo-conductor 41. In the operation of this system, if the line voltage increases, the current through incandescent lamp 42 increases, brightening lamp 42 and causing photo-conductor 41 to decrease in resistance and thereby shunt more of the available charging current away from capacitor 11. This slows the voltage buildup'across capacitor 11, thus delaying the firing of triac 5 and regulating the power delivered to lamp 1. A decrease'in line voltage operatesconversely to advance the firing of triac 5 to prevent a decrease in power supply to lamp 1. Resistance 43, as shown, may be a variable resistor'for setting the nominal power level in'lamp 1. Resistance 44 provides a fixed resistance for limiting the dissipation in the variable resistance 43.

Capacitor 36 in series with photo-conductor 41 functions to vary the effective charging time of capacitor 11. Inductor 12 arranged in series with charging capacitor 11 serves to shape the gate pulse current applied to triac 5 to make it compatible with the operational characteristics of the triac, while'inductor 23 arranged in series with charging capacitor 20 in the high voltage generating circuit serves to limit the rate of rise of the initial charging current through the'high voltage generating circuit for the purpose of protecting triac 5. Resistance 21 in series with capacitor 20 and inductor 23 serves to limit the magnitnde of the initial charging current for further protection of triac 5. Resistance is preferably arranged in parallel with charging capacitor 11 in the actuating circuit to provide stabilization of the triggering action. Power factor improvement is provided in the circuit by capacitor 22 connected across the source terminals as shown.

To provide for manually varying the light level of lamp 1 to the desired brightness, it is possible to arrange a variable resistor orpotentiometer (at a remote location, if desired) connected across the charging circuit which includes capacitor 11, so as to vary the effective charging time of the latter and thereby vary the power applied through switch 5 to the lamp. However, in the case of certain types of gaseous discharge lamps, such as the sodium vapor lamp mentioned (which is commercially available under the trademark Lucalox), manual adjustment of such avariable resistor to dim the lamp may be too rapid, resulting in extinguishing of the lamp because the arc voltage does not decrease as rapidly as the applied voltage. The reason for this is that the lamp arc voltage is a function of many variables, such as temperature, pressure and current density. Lamps of the type mentioned are characterized by arc voltages having a re-ignition peak which is primarily a function of deionization time of the lamp at current zero. A reduction of the applied voltage for a longer time period, as in the phase controlled ballast circuit described, results in greater deionization and hence a higher re-ignition voltage level. It has been found that extinguishing of the arc of sodium vapor lamps under these conditions may be avoided by allowing time for the arc temperature and pressure to decrease sufficiently to lower the re-ignition peak level.

In accordance with the present invention, the afermentioned difficulty is avoided in a simple and practical manner by the provision of a constant speed motor driving a potentiometer connected across the phase control actuating circuit. For this purpose there is provided, as shown in the illustrated embodiment, a potentiometer 50 connected across the capacitor 11 charging branch via a relay switch contact 51a operated by relay 51. In the inoperative condition of the dimming system of which relay 11 is a part, the feedback branch which contains photo conductor 41 and charging capacitor 36 is connected to the junction of resistors 10 and 17 via the normally closed relay contact 51a, so that the phase-controlled lamp operating circuit operates as described above. Relay 51 is connected to a voltage source, e.g., volts A-C, at terminals 52, and a manual switch 54 arranged in the line for energizing or de-energizing relay 51 as shown. When switch 54 is placed in the on position, relay 51 is energized, and operates to open normally closed connection in the feedback branch of photo-conductor 41 and capacitor 36, and close the connection in the dimming system branch containing potentiometer 50 with charging capacitor 36' in series therewith so as to connect this branch across the capacitor 11 charging branch. Thus, potentiometer 50 and capacitor 26, in effect, are substituted for photo-conductor 41 and capacitor 36. Potentiometer 50 is adjustable by means of constant speed motor 55, the driving shaft 55a of which is coupled to wiper arm 50a of potentiometer 50. Constant speed motor 55, which may be of any conventional or known type wherein the drive shaft speed is relatively constant, is a bi-directional motor having two windings which respectively turn the motor shaft 55a in opposite directions. The arrangement is such that winding 56- (also designated B) turns the motor shaft for moving potentiometer wiper arm 50a in the direction of the arrow designated B for increasing the brightness of lamp 1, whereas winding 57 (designated D) turns the motor shaft in the opposite direction to move arm 50a in the direction of arrow D for dimming lamp 1.

Motor windings 56, 57 are connected to the line as shown by push button actuating switches 58, 59, respectively, shown in their normal positions. The arrangement is such that with switch 54 on, when dimmer button 58 is pushed in, winding 57 of the motor is energized, whereas when brightening button 59 is pushed in, winding 56 is energized.

In a typical case, motor 55 turns at a speed of 2 revolutions per minute and the resistance member of potentiometer 50 is in the form of nearly a single turn, so that the time elapsing from full dimming to full brightness, or vice versa, is about 30 seconds.

To limit the travel of wiper arm 55a at the opposite ends of the potentiometer resistor, normally closed contacts 60, 61 are arranged in series with the respective motor windings and actuated by suitably arranged posi tion switches (not shown) at the opposite limits of one turn of motor shaft 55a. Thus, contact 61 is opened to de-energize winding 57 when arm 50a reaches its limit of travel in the direction of arrow D, whereas contact 60 is opened to de-energize winding 56 when arm 50a reaches its limit in the opposite direction.

With switch 54 in the off position as shown, the dimming system is inoperative since relay 51 is de-energized and contact 51a is in the position shown disconnecting the dimming system from the lamp operating circuit. However, in this condition the brightness winding 56 is connected to the supply source by conductor 62, so as to ensure that the motor is in full brightness position to facilitate starting of the lamp load when the lamp is restarted after having been extinguished by removal of source power.

As will be evident from the foregoing description, the operation of the disclosed system is such that when switch 54 is placed in the on position, relay 51 moves contact 51a from its normal position as shown to its other position connecting the potentiometer branch to the charging capacitor 11 branch. When button 58 is then pushed to dim lamp 1, energy is supplied to winding 57 which results in moving wiper arm 50a in the direction of arrow D, so as to decrease the amount of resistance of potentiometer 50. Due to the decreased resistance in this branch, more of the available charging current is shunted away from capacitor 11, resulting in slowing the voltage buildup across capacitor 11, thus delaying the firing of triac 5 and reducing the power delivered to lamp 1 and thereby causing it to become dimmer. Conversely, an increase in resistance supplied by potentiometer 50 through actuation of push button 59 results in advancing the firing of triac 5 and thereby increasing the brightness of lamp 1.

As will be understood by those skilled in the art, a plurality of lamps may be operated in similar fashion by employing ganged potentiometers coupled to the constant speed motor drive and with the lamps and ballasts therefor arranged in parallel.

Although the invention has been described as applied to a specific form of phase-controlled switching means for operating gaseous discharge lamps, it will be understood that it is also applicable to various other forms of such switch means, as, for example, disclosed in Nuckolls Pats. 3,249,807, 3,328,673, and 3,344,310.

While the present invention has been described with reference to particular embodiments thereof, it will be understood that numerous modifications may be made by those skilled in the art without actually departing from the scope of the invention. Therefore, the appended claims are intended to cover all such equivalent variations as come within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

-1. Lamp control circuit comprising, in combination, an alternating current source, gaseous discharge lamp means energized by said alternating current source, phase controlled switching means connected between said alternating current source and said gaseous discharge lamp means for controlling the energy supplied to said lamp means, actuating means connected to said alternating current source and said switching means for controlling the operation of the latter means, and controlled dimming means connected to said actuating means for varying the energy supplied to said lamp means at a predetermined maximum rate for selectively dimming and brightening said lamp means without extinguishing the same.

2. A device as defined in claim 1, said controlled dimming means comprising variable resistance means connected to said actuating means for controlling the operation thereof, driving means for selectively adjusting said variable resistance means at a predetermined maximum rate, and conductor means for connecting said driving meats to a source of alternating current.

3. A device as defined in claim 2, including second switching means connected to said conductor means for selectively connecting said variable resistance means to said actuating means and disconnecting the same therefrom.

4. A device as defined in claim 3, said second switching means comprising relay means for connecting said variable resistance means to said actuating means when said relay means is energized and for disconnecting the same when said relay means is de-energized.

5. A device as defined in claim 4, said phase-controlled switching means comprising bi-directional controlled semiconductor switch means having control electrode means to render the same conductive in either direction, said actuating means comprising a charging capacitor and a voltage sensitive switch in series discharge relation connected to said control electrode means for triggering said semiconductor switch means into conduction in opposite directions on alternate half-cycles, said controlled dimming means including a second charging capacitor in series with said variable resistance means connected across said first mentioned charging capacitor.

6. A device as defined in claim 2, said driving means comprising a constant speed motor operatively connected to said variable resistance means. 7

7. A device as defined in claim 6, said constant speed motor being turnable in opposite directions for selectively adjusting said variable resistance means in opposite directions, and manually operable switch means connected to said motor for selectively operating the latter in opposite directions.

. 8. A device as defined in claim 7, relay means connected to said conductor means for selectively connecting said valuable resistance means to, and disconnecting it from, said actuating means, main switch means connected to said conductor means and movable between a first position connecting said relay means and said manually op erable switch means to said conductor means and a second position disconnecting said relay means and said manually operable switch means from said conductor means.

9. A device as defined in claim 8, and means connecting said conductor means to said constant speed motor References Cited UNITED STATES PATENTS 3,317,789 5/1967 Nuckolls 315-199 X 3,328,673 =6/1967 Nuckolls 315--200 X 3,344,310 9/1967 Nuckolls 3 l5194 X 3,344,311 9/1967 Nuckolls 315-199 X JOHN W. HUCKERT, Primary Examiner A. J. JAMES, Assistant Examiner US. Cl. X.R. 

